1. Field of the Invention
The present invention relates to a toner for developing an electrostatic charge image and an image forming method employing the same.
2. Relation Art
A dry developing system employing a magnet brush is usually utilized for an electrophotographic image forming method using an electrostatic charge image developing toner from the view point of simplicity. In the field of the technology of the electrophotography, development competition of a compact color printer capable of forming a high quality image with high speed is become severe.
A cleanerless process is cited as a technique for realizing the compactness of the color printer in which removing of the cleaner unit is made possible by applying the charging and developing bias while designing the transfer means to be simple and compact (Japanese Patent Publication Open to Public Inspection, hereinafter-referred to as Japanese Patent O.P.I. Publication No. 2002-132015).
As to solving the above subject regarding the apparatus, an image forming method employing a polymerized toner prepared by a polymerization method is noted since a high quality toner image excellent in the fine line reproducibility is obtained when the image formed by the use of a small particle diameter polymerized toner having a sharp distribution of particle diameter and that of shape (Japanese Patent O.P.I. Publication No. 2000-214629, equiv. U.S. Pat. No. 6,296,980).
The polymerized toner is advantageous for making compact the apparatus since in such the toner, the charge of the toner particles is uniform so as to obtain high transference ability can be obtained and the toner has suitability to the cleanerless process.
Many kinds of external additives tend to be added to the polymerized toner for raising the transferring ability. In the process employing the usual cleaning system, many kinds of external additive are also employed.
By the addition of the large amount of the external additive, a problem is caused that the adhering and fixing strength of the external additives on the toner particle surface is weak and the external additives are easily released from the toner particle.
The reason of such the problem has been considered that the majority of the toner particles prepared by the polymerization method have no corner on the surface thereof so that the external additives can not be strongly trapped on the toner particle surface.
The problems posed by the releasing of the external additive from the toner particle are cited as follows.
(a) In the case of a double-component developer, for example, the external additives released from the toner particles are moved to the carrier or the surface of a developing roller having a triboelectric charging member and the triboelectric charge is hindered by the contamination of them so as to cause insufficient charging. As a result of that, the life of the developer and the developing device is shortened.
(b) The released external additive is stuck or polishes the surface of the heating roller of the fixing device or the photoreceptor and causes an irregular point (such as a damage). The toner offset or insufficient lowering of the potential occurs at the irregular point and faults so called in the field of the art as the black spot or white spot are formed.
(c) The released external additive contaminates the charging device and the insufficient charging occurs at the contaminated portion and white a halftone line image is resulted.
The released external additive contaminates the surface of the carrier and causes fluctuation or rising of the charged potential particularly under a low temperature and humidity condition so as to form fogging of the image.
A large diameter external additive considerably causes the problems of releasing since the adhering and fixing force of such the additive is weak even though such the additive has a merit on the transfer development. Here, the large diameter external additive is supposed particles having a primary particle diameter of from 40 to 1,000 nm.
Large particle diameter silica is effective to strengthen the adhering and fixing force of the external additive with the toner particle. However, the large particle diameter silica shows high charging ability and causes a problem of the increasing in the charging amount of the toner, and such the silica further causes problems, when it is employed in combination with a small diameter photoreceptor, that peeling discharge tends to occur on the occasion of the separation of the image receiving material from the photoreceptor by which unevenness in the halftone image (frequently called as transfer repelling in the field of the art) tends to occur. Such the problems become remarkable under the low temperature and humidity condition.